What Causes Cancer?

Ultraviolet light, tobacco, and other carcinogens are known to trigger DNA mutations that cause cancer. But which mutations and why?

December 1, 2016

The planar green and white molecule at the center is a modified form of a carcinogen found in cigarette smoke, among other sources. It distorts the natural shape of DNA, causing errors whenever the DNA is read or copied.CREDIT: Zephyris/Wikimedia Commons

After decades of frustration, investigators might now be getting what they need most: a solid lead.

Los Alamos researcher Ludmil Alexandrov uses advanced supercomputers to examine the full genomes of tumor cells and identify mutational patterns. To date, he has analyzed genomes from 12,023 samples spanning 40 different human cancers and identified more than 8 million distinct mutations. But mutations alone do not necessarily constitute cancer, and from these 8 million mutations, he has identified 30 “mutational signatures”—recurring combinations of mutations that act like genetic fingerprints for various human cancers. Some signatures correspond to known cancer-causing defects in the genome. Others correspond to known or suspected carcinogens. Others still remain a complete mystery.